A preferred embodiment proof of delivery system for use with a solid product dispenser includes an outlet conduit and a sensor mechanism. The outlet conduit is light transmissive and includes an interior surface and an exterior surface. The interior surface is exposed to humid conditions. The sensor mechanism is proximate the exterior surface of the outlet conduit, and the sensor mechanism senses delivery of a solid product through the outlet conduit. The outlet conduit provides a barrier to the humid conditions thereby protecting the sensor mechanism from exposure to the humid conditions.